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Commit 5b206d48 authored by Frederic Weisbecker's avatar Frederic Weisbecker
Browse files

vtime: Update a few comments 



Update a stale comment from the old vtime era and document some
locking that might be non obvious.

Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Kevin Hilman <khilman@linaro.org>
parent 2d854e57

include/linux/context_tracking.h

+4 −6
Original line number Diff line number Diff line
@@ -72,8 +72,9 @@ extern void guest_exit(void); 
static inline void guest_enter(void)

{

	/*

	 * This is running in ioctl context so we can avoid

	 * the call to vtime_account() with its unnecessary idle check.

	 * This is running in ioctl context so its safe

	 * to assume that it's the stime pending cputime

	 * to flush.

	 */

	vtime_account_system(current);

	current->flags |= PF_VCPU;
@@ -81,10 +82,7 @@ static inline void guest_enter(void) 


static inline void guest_exit(void)

{

	/*

	 * This is running in ioctl context so we can avoid

	 * the call to vtime_account() with its unnecessary idle check.

	 */

	/* Flush the guest cputime we spent on the guest */

	vtime_account_system(current);

	current->flags &= ~PF_VCPU;

}

kernel/sched/cputime.c

+7 −0
Original line number Diff line number Diff line
@@ -712,6 +712,13 @@ void vtime_user_enter(struct task_struct *tsk) 


void vtime_guest_enter(struct task_struct *tsk)

{

	/*

	 * The flags must be updated under the lock with

	 * the vtime_snap flush and update.

	 * That enforces a right ordering and update sequence

	 * synchronization against the reader (task_gtime())

	 * that can thus safely catch up with a tickless delta.

	 */

	write_seqlock(&tsk->vtime_seqlock);

	__vtime_account_system(tsk);

	current->flags |= PF_VCPU;